The present application is generally related to inground operations and, more particularly, to advanced systems, apparatus and methods for performing such inground operations in ways that are heretofore unknown.
A technique that is often referred to as horizontal directional drilling (HDD) can be used for purposes of installing a utility without the need to dig a trench. A typical utility installation involves the use of a drill rig having a drill string that supports a boring tool at a distal or inground end of the drill string. The drill rig forces the boring tool through the ground by applying a thrust force to the drill string. The boring tool is steered during the extension of the drill string to form a pilot bore. Upon completion of the pilot bore, the distal end of the drill string is attached to a pullback apparatus which is, in turn, attached to a leading end of the utility. The pullback apparatus and utility are then pulled through the pilot bore via retraction of the drill string to complete the installation. In some cases, the pullback apparatus can comprise a back reaming tool which serves to expand the diameter of the pilot bore ahead of the utility so that the installed utility can be of a greater diameter than the original diameter of the pilot bore.
Such trenchless utility installation is generally well suited to developed areas as compared to the prior practice of digging a trench along the entirety of the installation pathway. HDD has also proven to be practical for installing utilities in locations where a trench cannot be formed such as, for example, under a river, under a building or below some other obstruction, man-made or otherwise. Unfortunately, there are some risks associated with trenchless utility installation. For example, there may be pre-existing utilities that cross an intended path of installation of the new utility. In some cases, the locations of pre-existing utilities are known, however, that is not always the case. Thus, there is a danger associated with inadvertently drilling into an unknown pre-existing utility. The prior art includes several approaches that attempt to deal with this problem, as will be described immediately hereinafter.
One approach is taught by U.S. Pat. No. 5,457,995 issued to Staton (hereinafter, the '995 patent). Staton attempts to use acoustical information in conjunction with seismic information in order to detect that a boring tool has encountered a pre-existing utility. Unfortunately, the technique requires prior knowledge of the pre-existing utility as well as physical access thereto. For at least these reasons, the technique is not applicable for purposes of detecting an encounter with an unknown pre-existing utility. It is noted that the patent briefly describes monitoring thrust force that is applied to the drill string for use in conjunction with acoustical and seismic information. In particular, the '995 patent describes monitoring hydraulic thrust force at the drill rig as assertedly being indicative of striking a utility based on an increase in the thrust force. At the same time, however, the '995 patent admits that there may be no increase in the thrust force, depending upon the material from which the utility is formed, and does not appear to offer any solution in this instance. Applicants further recognize, as will be described in detail hereinafter, that thrust force at the drill rig does not necessarily indicate the force that is being applied to the soil by a boring tool.
Another approach taken by the prior art is described by U.S. Pat. No. 6,614,354 (hereinafter, the '354 patent). This patent teaches a technique for detecting contact with an inground pipeline based on monitoring an acoustic sensor and an impressed current sensor. Unfortunately, like the '995 patent, prior knowledge of the existence of the pipeline as well as physical access are required in order to use the technique.
During an HDD operation, either for purposes of drilling the pilot bore and during pullback or back-reaming to install the utility, a drilling fluid or mud is typically transmitted through the drill string for emission from the inground end. During drilling, the mud can be emitted under such high pressure from the drill head that it assists in cutting through the soil and/or rock at the end face of the pilot bore. The mud can then flow in an opposite direction, back to the drill rig, in an annular region surrounding the boring tool and drill string while carrying cuttings back to the surface. The drilling mud can also serve in cooling the drill head and providing lubrication. During the pullback/back-reaming operation, drilling mud can be emitted from a leading surface of a reaming tool under high pressure, as the drill string is retracted, to assist in cutting through the soil and to provide lubrication for the utility that is being installed so as to reduce the tension on the utility. As in the drilling operation, the drilling fluid can also serve to carry cuttings in the uphole direction.
In view of the foregoing, another risk that is associated with trenchless utility installation involves what is often called a “frac-out.” Rather than follow the uphole path that is defined by the pilot bore after emission from the inground tool, the pressurized mud can sometimes escape through a fracture in the ground. The escaped mud may damage roadways or other structures and may raise environmental concerns. As will be described in detail below, Applicants further recognize heretofore unseen methods and apparatus for purposes of frac-out detection. Still further benefits are described below in relation to the described techniques for frac-out and cross-bore detection. For example, certain operational conditions associated with the emission of the drilling mud from drill head jets can be detected.
Still another risk with respect to trenchless utility installation concerns what can be referred to as key-holing. The latter term describes the behavior of the utility in tending to straighten curves during the pullback operation. Applicants recognize that the result of key-holing can be an undesirable intersection between a new utility and a pre-existing utility or other inground obstacle. Applicants further recognize and describe below heretofore unseen methods and apparatus for purposes of detecting key-holing.
A number of other improvements are brought to light in the disclosure of the present application. For example, improvements are described relating to system communication and determination of the depth of the inground tool as well as an advanced steering technique that is applicable to inground conditions that traditionally result in difficulties with respect to steering the boring tool.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.